The invention relates to the field of air purification. It relates to an impregnated filter material, as well as to a method for manufacturing an impregnated filter material, according to the preamble of the respective, independent patent claims. The filter material according to the invention is particularly suitable for the adsorption of noxious substances and/or toxins, out of respiratory air, thus for the application for example in protective masks for personal protective equipment or in filters of ventilation facilities in the field of collective protection.
According to the state of the art, activated carbon or another suitable base material with a large surface area per unit of weight is applied, in order to create base materials for example for protective mask filters. For this purpose, the base material is usually impregnated with metals, for example in the form of metal oxides, carbonates or chlorides, and, as the case may be, with additional organic substances, by which means it obtains an increased, as the case may be, specific adsorption capacity, which at least partly is based on the metals catalysing chemical conversions of the noxious substances, or the chemisorption of the base material being changed or improved. Such an impregnated base material, in particular an activated carbon impregnated in such a manner, is suitable for the removal for example of noxious substances such as chlorine, hydrogen chloride, hydrogen cyanide, hydrogen sulphide, carbon tetrachloride, ammonia etc., from respiratory air.
Base materials based on activated carbon were used in protective mask filters during the Second World War, wherein the activated carbon was impregnated with copper, silver and chromium, and on account of this were particularly effective against hydrogen cyanide, cyanogenic compounds and arsenics. However, since chromium+6 is less desirable for ecological reasons due to its carcinogenic characteristics and due to its water solubility, later and still up to this present day, one has attempted to replaced chromium+6 in the impregnating means.
According to U.S. Pat. No. 4,801,311 (Westvaco Corp.), a vanadate or a molybdate is used for the impregnation of activated carbon instead of chromium, wherein the activated carbon additionally comprises triethylene diamine and, as the case may be tartaric acid. According to EP0450414 (Drägerwerk), a chromium-free activated carbon is manufactured by way of impregnating the activated carbon with copper and tin as well as tungstate or molybdate and, as the case may be, vanadate. According to EP0614400 (Calgon Carbon Corp.), a chromium-free activated carbon is manufactured by way of impregnating the activated carbon with copper or zinc as well as molybdate. According to the mentioned publications, the effect of the chromium-free activated carbons is just as good as those activated carbons which are impregnated with chromium, in particular concerning the adsorption of hydrogen cyanide and cyanogenic compounds, and concerning the storage capability.